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Benefits of Retiming Traffic Signals, The
Institute of Transportation Engineers. ITE Journal, Apr 2004 by Sunkari, Srinivasa
* The need for costly reconstruction can be postponed or eliminated by providing improved flow using existing resources in a more cost efficient manner.
* Changes in traffic flow for different times of day or days of the week can be accommodated.
* Signal retiming should be conducted during a reconstruction project when a lane closure or traffic detour causes a significant change in demand or capacity.
* Signal retiming is a cost effective method to improve traffic operation. It can produce benefit to cost ratios as high as 40:1.
HOW IS SIGNAL RETIMING CONDUCTED?
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Signal retiming determines the timing to be entered in a controller using a series of calculations performed by a traffic engineer. The method for conducting signal retiming can be summarized as follows:
* An inventory of the system is conducted to determine geometric conditions and other pertinent information and to gather field observations of current traffic conditions during peak traffic periods.
* Traffic and pedestrian volume data are collected. Traffic counts include all turning and through movements as well as a classification of vehicles and the number of pedestrians using each crosswalk for each 15-minute interval of the study period. Travel time data also are collected for travel from one end of the system to the other, to identify current operating conditions.
* A collision history and analysis are prepared. Collision records for the past three years are obtained. An analysis is conducted by preparing a collision diagram and causation, collision types and remedy tables to determine if a change in signal operation is likely to provide safer operation.
* Collected data are processed and analyzed using capacity analysis, traffic signal timing optimization and simulation software programs. The model is calibrated using existing timing and the variables are adjusted to determine optimum signal timing.
* Improved coordination offsets through a series or group of signals are determined using signal coordination software programs such as SYNCHRO or PASSER II. The results also may be tested using simulation software programs such as CORSIM.
* The new timing is implemented at the intersection(s).
* The new timing is evaluated in the field during various critical time periods and final adjustments arc made. Travel time and delay studies are conducted when the final timing plans are in place. Before-and-after studies are conducted through the groups of signals to determine and document the improvement in traffic flow.
* The process is repeated every three to five years, or more frequently based on changing conditions, to assure the continued optimum flow of traffic.
WHO RETIMES TRAFFIC SIGNALS?
Typically, the ultimate responsibility for signal retiming falls to the agency responsible for the operation of the roadways where signals are located.
On state highways, state departments of transportation (DOT) usually have responsibility for the timing and operation of signal equipment and are tasked with the goal of providing optimal traffic flow. In their timing efforts, the state highway systems usually have priority.
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